Conventionally, systems have been employed to electronically monitor a series of unattended remote locations. Common types of monitoring systems use a group of sensor switches, such as fire alarm or motion detection switches, positioned at the desired locations.
Often a series of unattended doors and windows must be electronically monitored by a security system employing a group of motion detection switches for sensing the opening and closing of the respective doors and windows. Another application generally requiring a large number of sensor switches is the field of fire prevention where a group of alarm switches must be monitored for proper operation.
Since the reliability of a fire or security system is often the primary concern of the user, monitoring the status of the remote sensor switches employed in such systems for both normal and abnormal operation becomes extremely important.
Of course, maintaining system reliability becomes even more difficult as the number of sensor switches employed in a system increases. Even a single undetected switch fault adversely impacts on the reliability. If a faulty sensor switch fails to detect the unauthorized opening of a door, user confidence is eroded and the system is of little value. Consequently, reliable monitoring requires systematic detection of both fault and tampering conditions for each and every sensor switch used in the system.
In order to provide effective monitoring, different types of fault conditions must also be detected and distinguished. Installation of a security system often requires the connection of sensor switches to unique pairs of a series of coded wires. Because installation faults such as reverse connections or cross wirings will occasionally occur, monitoring the switch locations for proper installation is certainly desirable.
Even when properly installed, however, a malfunction may still occur through inadvertent grounds or shorts to the system conductors. Prompt detection by the monitoring system not only of the existence of a short but also the location of the short enables efficient repair to the system and greatly reduces system down time.
Another problem which might arise is tampering to the security or alarm system. In order to be effective, the monitoring system must be able to detect acts of tampering which defeat the normal operation of any sensor switch. Since tampering often involves the shorting of a sensor switch or the grounding of conductors leading to the switch, such occurrences must be sensed and detected to maintain system reliability.
In accordance with the present invention, an effective system is provided for electronically monitoring the status of a group of switches at remote locations. The system permits accurate and reliable monitoring of installation faults, inadvertent grounds and shorts, as well as unauthorized alterations to the system caused by tampering.